feat: psql import

[cristianmtr]

• adding an import from PSQL (to avoid dumping to disk stage)
• PSQL distributes data to virtual shards, to prepare for shard allocation
• snapshotting the table state
• getting the document changes since timestamp
• soft deletion in PSQL
• [x] add cleanup endpoint. And make cleanup happen before snapshot
• [x] implement full syncing via delta
• [x] more parametrization at init